High-profile death row inmate killed in prison yard attack

California prison officials are investigating a fatal stabbing at Calipatria State Prison that claimed the life of a 46-year-old inmate sentenced to death for his role in a high-profile kidnapping and murder case.

Alberto Martinez, originally from Castaic, was pronounced dead at 2:20 p.m. after an attack involving three other inmates, according to the California Department of Corrections and Rehabilitation. Martinez was serving time for his involvement in the 2002 abduction and killing of David Montemayor, a Buena Park businessman.

Prison staff reported observing Tyler A. Lua strike Martinez and knock him to the ground at approximately 1:23 p.m. Two other inmates, Jorge D. Negrete-Larios and Luis J. Beltran, then allegedly began striking Martinez as he lay motionless. Corrections officers intervened using pepper spray and a baton strike to halt the assault.

Martinez sustained injuries consistent with an incarcerated-manufactured weapon, and two such weapons were recovered from the scene. He was transported to the prison's triage and treatment area, where life-saving measures were unsuccessful.

The victim had been on death row since 2010 after being convicted of first-degree murder, attempted first-degree murder, conspiracy to commit murder, and street terrorism. His convictions stemmed from his role as the getaway driver in the Montemayor case, which prosecutors argued was orchestrated by the victim's sister over a family business dispute.

Lua, 25, Negrete-Larios, 33, and Beltran, 31, the alleged assailants, are serving sentences for various violent crimes, including attempted murder and firearms offenses. They have been placed in restricted housing pending an investigation by the prison's Investigative Services Unit and the Imperial County District Attorney's office.

The incident has been reported to the Office of the Inspector General, and the Imperial County Coroner will determine the official cause of Martinez's death. Authorities at the prison have limited access to the yard where the attack took place while the inquiry is ongoing.